DESCRIPTION: The mammalian intestinal epithelial cells develop along 3 major axes: (1) the longitudinal duodenum-to-colon axis, (2) the vertical crypt-to-villus axis, and (3) the temporal axis during development. The process of differentiation into each of the components of these axes is dependent on a specific program of gene expression that is unique to that cell type and location. The investigator proposes the adenosine deaminase gene as a model system in which to investigate the network regulating gene expression along the various axes in the small intestine. He has shown that high levels of ADA mRNA are present in the duodenum where they are limited to the villus enterocytes. He has also provided preliminary evidence from transgenic mouse experiments that the duodenal-specific regulation of the ADA gene is located in an intragenic segment, probably in intron 2. Three specific aims are proposed: (1) to characterize the duodenal-specific regulatory region within the ADA gene, including a putative duodenal-specific enhancer element, (2) to identify and characterize the duodenal-specific factors which bind to the enhancer element identified in (1), and (3) to identify and characterize the mouse ADA gene duodenal-specific regulatory element.